Hybrid energy storage devices, also known as asymmetric supercapacitors or hybrid battery/supercapacitors, combine battery electrodes and supercapacitor electrodes to produce devices having a unique set of characteristics including cycle life, power density, energy capacity, fast recharge capability, and a wide range of temperature operability. Hybrid lead-carbon energy storage devices employ lead-acid battery positive electrodes and supercapacitor negative electrodes. See, for example, U.S. Pat. Nos. 6,466,429; 6,628,504; 6,706,079; 7,006,346; and 7,110,242.
The conventional wisdom is that any new battery or supercapacitor technology assembles components and uses techniques that are unique to that technology. Moreover, the conventional wisdom is that lead-carbon energy storage devices are required to be assembled using relatively high compression of the cell or cells within the device. The high compression is due in part to the large contact resistance existing between an activated carbon active material and a current collector of a negative electrode. It is also conventional wisdom that equipment generally used to manufacture conventional lead-acid batteries and commonly employed in the automotive industry, motive power, stationary, and other energy storage applications cannot be employed in the production of hybrid energy storage devices.
It is a purpose of the present invention to provide hybrid energy storage devices having excellent cycle life and which are capable of being manufactured using available conventional lead-acid battery manufacturing equipment. The inventors have proven that single and multi-cell hybrid energy storage devices may be manufactured using conventional lead acid-battery manufacturing equipment with modifications owing to the design of the negative electrode that eliminates the need for large amounts of stack pressure to be applied to cells within the device.
Thus, contrary to conventional wisdom for hybrid energy storage devices, a high compression is not required in the assembly of a hybrid storage device according to the present invention. It is unnecessary to provide an additional mechanism to compress individual cells, and the hybrid energy storage devices can be assembled with commercially available cases and covers. Otherwise, new custom hardware and assembly equipment is required, leading to significant cost increases and/or significant process changes.